RESUMO
The aim of the present study was to characterize the effect of oxidative stress on iron reduction rates in biological systems. The tested oxidative stress conditions included acute iron overload in rats, UV-B irradiation in algae cultures and leaves, and paraquat treatment and aging in soybean embryonic axes upon imbibition. Treatment of rats with iron-dextran resembles hemochromatosis secondary to iron loading anemias and high oral iron intake. A significant increase was detected in both iron deposits in liver cells and microsomal iron content after 4 h of a single dose of iron-dextran, however, the iron reduction rate was not affected in the presence of either NADPH or NADH as cofactor. In vivo iron reduction rate in Chlorella vulgaris cells was not significantly different in log and stationary phases. Exposure of the cultures to UV-B doses of O.8 and 4.4 kJ/m2 increased iron reduction rate by intact cells from 6 (control) to 32 and 64 nmol/lO(9) cell.min, respectively. UV-B exposure of soybean leaves lead to a significant increase in leakage of electrolytes probably due to membrane damage, however, iron reduction rates were not significantly different in control and irradiated leaves. Soybean embryonic axes incubated in the presence of paraquat or axes from aged seeds showed a significant decrease in fresh weight of the axes after 30 h of development. Moreover, the consistent increase in iron reduction rates measured in control axes during the imbibition period was inhibited either in the presence of paraquat or with aged embryonic axes. The data presented here suggest that iron reduction does not seem a universal early index of oxidative damage in biological systems, in spite of its crucial role in oxidative metabolism.